1. Field of the Invention
The present invention relates to an apparatus for forming reduced pressure and for processing an object. More particularly, it relates to a heat insulating structure in the process chamber of the magnetron plasma etching apparatus and a heat insulating structure provided between the process chamber and a load lock chamber.
2. Description of the Related Art
Various kinds of apparatus have been proposed to apply various kinds of process to semiconductor wafers in a vacuum chamber. Particularly in the course of manufacturing semiconductors, the semiconductor wafers are subject to various kinds of thermal influence at the etching, ashing and film-forming processes.
In the case of the plasma etching apparatus, for example, plasma of high temperature is generated because of the anisotropic etching conducted and various kinds of thermal damage are added to the semiconductor wafers because of the radiation heat of the plasma. In order to solve this, a susceptor is cooled by a lower cooling jacket to indirectly cool the semiconductor wafer. The susceptor is exposed, in this case, to process atmosphere in the chamber only at the top (on which the wafer is mounted) thereof but not at the other areas (or side and underside) thereof. In addition, the outer circumferences of the susceptor and the cooling jacket are located in the process chamber and the underside of the cooling section is connected to the process chamber with air interposed between them.
The chamber which encloses the outer circumferences of the susceptor and the cooling section is opposed to them with an insulating matter such as ceramics interposed between them and in the case of the plasma etching of the RIE type, the susceptor is used as an RF cathode and the wall of the chamber is grounded. No attention is paid to heat transmission between the susceptor/cooling section and the chamber wall in this case. The amount of heat entered from the chamber wall into the cooling section is thus made large. This causes the wafer to be insufficiently cooled, and the temperature of the chamber wall to be lowered to a great extent.
When the temperature of the chamber wall is lowered, various kinds of fliers caused during the plasma etching process adhere to the inner wall of the chamber, which is thus contaminated. When the inner wall of the chamber is contaminated in this manner, the fliers adhered are scattered from the inner wall of the chamber was into the air in the chamber to adhere to the wafer, thereby causing the capacity of processing the wafers in the chamber to be lowered. In addition, maintaining care must be often added to the process chamber.
The temperature to which the wafers are cooled is now set to be in a range of -60.degree. C. to -100.degree. C., but as the temperature at which the wafers are processed becomes lower and lower, it will be thought to reach -150.degree. C. This will cause the inner wall of the process chamber to be more often contaminated in the future.
In order to prevent the inner wall of the process chamber from being contaminated, therefore, a heater is embedded in the wall of the process chamber to positively heat the wall.
In the case of the pressure-reduced processing apparatus of this kind, however, load lock chambers are located adjacent to the process chamber. Each of the load lock chambers is communicated with an exhaust means, which allows pressure in the load lock chamber to be reduced to the internal pressure in the process chamber for a short period. When the wafer is carried into and out of the process chamber via the load lock chambers, dust and particles can be prevented from entering into the process chamber.
The process and load lock chambers are usually made of metal such as aluminum and they are bolt-fixed to each other with their metal faces contacted at such a position that their gates are opposed to each other. This causes the amount of heat transmitted from the process chamber wall to the load lock chamber wall to become large. In other wards, the heat capacity of the process chamber wall becomes large. It therefore needs quite a large heating power and a long time to heat the process chamber to a predetermined temperature.
In addition, temperature control for keeping the process chamber wall at the predetermined temperature is quite difficult.
Further, each of the load lock chamber is provided with a handling system (having robot) arms for carrying the wafer into and out of the process chamber and as the temperature of the load lock chamber is raised higher and higher by heat transmitted from the process chamber, the drive section of the handling system is worn more and more. The amount of dust thus created in the load lock chamber becomes unnegligible, thereby lowering the capacity of processing the semiconductor wafers in the process chamber because of dust adhering to the wafers. In addition, the life of the handling system becomes shorter as the drive section thereof is worn more and more.